The present invention relates to a core such as a rotor core in a rotating electrical machine such as a motor and to a method for manufacturing the core.
For example, FIG. 5 shows one example of the configuration of a known conventional rotor core 31 of a motor. According to this conventional configuration, the rotor core 31 has multiple accommodating slots 32 arranged along the outer circumference. A permanent magnet 33 is accommodated in each accommodating slot 32. The space between the inner surface of each accommodating slot 32 and the associated permanent magnet 33 is filled with fixing agent 34 for fixing the permanent magnet 33 in the accommodated state. As the fixing agent 34, epoxy resin, which is a thermosetting resin, is generally used.
The rotor core 31 is typically manufactured according to the processes described below as shown in FIG. 6. In a first step 35, core sheets are formed by pressing and laminated to form a rotor core 31. In the next step 36, a permanent magnet 33 is inserted into and accommodated in each accommodating slot 32. In the subsequent step 37, the rotor core 31, which accommodates the permanent magnets 33, is heated to about 150° C. using, for example, a heating furnace. This is because, since epoxy resin, which is a thermosetting resin, is used as the fixing agent 34 for fixing the permanent magnets 33 in the accommodated state, the rotor core 31 and the permanent magnets 33 need to be preheated prior to injection of the fixing agent 34.
In the next step 38, with the rotor core 31 and the permanent magnets 33 heated, the space between the inner surface of each accommodating slot 32 and the corresponding permanent magnet 33 is filled with the fixing agent 34, which is made of epoxy resin, using, for example, a molding machine. As the fixing agent 34 hardens, the permanent magnets 33 are fixed in the accommodating slots 32 in the accommodated state. In the subsequent step 39, the rotor core 31, in which the permanent magnets 33 are accommodated and fixed, is cooled to ordinary temperature using, for example, a cooling furnace.
After being processed through the above described steps, the rotor core 31 is subjected to further steps including installing of a rotor shaft.
Further, Japanese Laid-Open Patent Publication No. 2010-141989 discloses a conventional rotor core used in this type of motor. In this conventional configuration, the permanent magnet accommodated in each accommodating slot of the rotor core is split into two or more pieces, and a foamed plastic sheet is provided between the magnet pieces. After the permanent magnets are inserted in the accommodating slots, the foamed plastic sheets are heated so that the thickness is increased due to thermal expansion. This presses the split magnet pieces against the inner surface of the accommodating slot so that the magnet pieces are fixed in an accommodated state.
The above described conventional configurations have the following drawbacks.
In the conventional configuration shown in FIGS. 5 and 6, epoxy resin, which is thermosetting resin, is used as the fixing agent 34 for fixing the permanent magnets 33. The configuration requires the heating step 37, which is performed prior to injection of fixing agent 34 to preheat the rotor core 31 and the permanent magnet 33, and the cooling step 39, which is performed after injection of the fixing agent 34 to cool the rotor core 31 and the permanent magnet 33. Thus, a relatively large number of steps are required for manufacturing the rotor core 31, and the facility for performing the steps tend to be large scale, accordingly.
In the manufacturing process of the rotor core 31, the magnet steel, which forms the permanent magnets 33, has a property of extending in the widthwise direction as indicated by arrows in FIG. 5 when the rotor core 31 and the permanent magnets 33 are cooled to ordinary temperature. Due to this property, stress may concentrate on the permanent magnets 33 or narrow parts 311 in the outer circumference of the rotor core 31, which can deform these parts.
Further, the conventional configuration disclosed in Japanese Laid-Open Patent Publication No. 2010-141989 has foamed plastic sheets, which function as fixing agent for fixing permanent magnets in the accommodating slots. Thus, the configuration has an increased number of components of the rotor core 31. Also, during manufacturing, a foamed plastic sheet needs to be arranged between the permanent magnet pieces, and the rotor core and the permanent magnets need to be heated with the foamed plastic sheets inserted in the accommodating slots, so that the foamed plastic sheets are thermally expanded in the direction of the thickness. Thus, this conventional configuration not only has complicated manufacturing process, but also requires heating and cooling steps as in the case of the previous conventional configuration shown in FIGS. 5 and 6. That is, a relatively large number of steps are required for manufacturing a rotor core.